Propellant mixing process



nitrocellulose.

United States Patent 3,041,216 PROPELLANT MIXING PROCESS Charles C.Bice, Bartlesville, Okla, assigner, by mesne assignments, to the UnitedStates of America as represented by the Secretary of the Air Force NoDrawing. Filed June 22, 1959, Ser. No. 822,149 8 Claims. (Cl. 149-1?)This invention relates to a propellant mixing process. In one aspectthis invention relates to a process for mixing solid composite typepropellants wherein an oxidizer component is dispersed in a rubberybinder component.

Rocket propellants have achieved considerable commercial importance aswell as military importance. Jet propulsion motors of the type in whichthe propellants of this invention are applicable can be employed to aida heavily loaded plane in take off. Said motors can also be employed asan auxiliary to the conventional power plant when an extra surge ofpower is required. Said motors can also be employed to propelprojectiles and land vehicles. Said propellants can also be used foruses other than propulsion. For example, they can be used as gasgenerators in starting devices, power units where a fluid is employed asa motive force, and other applications where a comparatively largevolume of gas is required in a relatively short period of time.

Solid propellants can be classified with respect to composition asdouble base type, single base type, and composite type. An example of adouble base propellant is ballistite which comprises essentiallynitroglycerin and Examples of single base propellants are nitrocelluloseand trinitrotoluene. Composite type propellants are usually composed ofa crystalline oxidizer component uniformly dispersed in a fuel matrixwhich is designated as a binder component. Said composite typepropellants may contain other materials to facilitate manufacture orincrease ballistic performance, such as a burning rate catalyst. Inrecent years binder com ponents comprising natural and/or syntheticrubber, together with a rein-forcing filler such as carbon black andother rubber compounding and vulcanizing agents, have been widely usedin composite type propellant-s.

Various processes have been proposed for blending the oxidizer componentand other dry ingredients into the binder component. In one widely usedprocess, fre quently referred to as the dry mix method, the oxidizercomponent and the other dry ingredients are slowly added continuously,or incrementally, to the binder component. Some solid propellantcompositions of the composite type are very diflicult, if notimpossible, to mix by said dry mix method. Difiiculties are encountered,particularly when the amount of oxidizer component and other dryingredients is high, such as above about 83 percent by weight. Forexample, excessive power may be required to drive the mixing equipment,the mixture may not be sufiiciently uniform when it appears to be mixed,or the mixture may be unsuitable for either extrusion or molding intopropellant grains.

In another mixing process frequently referred to as the solvent mixtechnique, the binder component is dis-' persed or dissolved in asuitable fluid which is a solvent for the rubber. The oxidizer componentand other dry ingredients can be readily mixed with the thus fluidizedbinder and the solvent is subsequently removed. This solvent mixtechnique assures a good mixture, i.e., uni form dispersion with lowpower requirements for the mixing. However, due to the relatively largeamounts of solvent required, solvent removal and recovery costs areappreciable and in many instances almost prohibitive. In the use ofsolid propellants as gas generators, and particularly for the propulsionof rockets and other missiles, maximum performance per unit weight ofpropellant is highly important. However, due to the abovedescribeddifliculties with many compositions, good performance is oftensacrificed in order to obtain a composition which can be readilyprocessed.

' I have found that the above-described difliculties can be eliminatedor at least mitigated, and such diificultly processable propellantcompositions can be mixed to contain high percentages of oxidizercomponent and other solid dry ingredients by first mixing a portion ofsaid oxidizer component and/or said other solid ingredients with thebinder component, then adding a relatively small amount of a solvent forsaid binder component, and then incorporating the remainder of saidsolid ingredients.

An object of this invention is to provide an improved propellantcomposition. Another object of this invention is to provide a processfor mixing composite type propellants. Another object of this inventionis to provide a process for mixing composite type propellants whichprocess is particularly suitable for propellants having high oxidizercontents or solids loadings. Still an-. other object of this inventionis to provide a process for mixing propellants of a composite typewherein a portion of the oxidizer component and/or other solidingredients is admixed with the binder component to obtain a powderymass, a relatively small amount of a solvent for the binder is thenadded to said powdery mass, the remainder or" said solid ingredients arethen incorporated in said binder, and said solvent is then removed.Other aspects, objects, and advantages of the invention will be apparentto those skilled in the art in view of this disclosure.

Thus, according to the invention there is provided a method forpreparing a solid composite type propellant wherein finely divided solidingredients comprising an oxidizer component are uniformly dispersed ina binder component comprising a rubbery polymer, which method comprisesthe steps of: mixing successive increments of said solid ingredientsinto said binder component until a powdery mass is obtained;incorporating a low boiling organic solvent into said powdery mass withsuflicient mixing to form a uniform intermediate dispersion; mixing atleast one additional increment of said solid ingredients into saidintermediate dispersion with sufiicient mixing to obtain a final uniformdispersion of said solid ingredients in said binder component; andremoving said solvent from said final dispersion.

In the practice of the invention the oxidizer, or oxidizer componenttogether with the other solid dry ingredients, is mixed with the bindercomponent gradually or in small increments until the amount of saidsolid components which have been added is sumcient to obtain a powderymass. The amount of said solid ingredients necessary to obtain a powderymass depends upon the type of rubbery polymer and its Mooney value, theamount and kind of rubber compounding ingredients which have beenincorporated in said rubbery polymer, and the particle size of saidoxidizer component and the other dry solid ingredients. Generally, thisamount falls in the range of 78 to 92 weight percent and more commonlywithin the range of 83 to 88 weight percent of the oxidizer content inthe propellant mixture. The exact amount necessary to obtain the powderymass can be readily ascertained by routine tests for any givenpropellant composition. As the oxidizer component and/or other solidingredients is added with continual mixing,

the mass in the mixing apparatus becomes more viscous, and more power isrequired to continue mixing. A point is reached where, upon the additionof more oxidizer, a powdery condition is obtained, i.e., the mass in themixer is transformed from a rubbery mass into a powdery mass. Thispowdery condition is reflected by a rather 'is usually in the suddendecrease in the power required to operate the mixing equipment. Theattainment of this powdery condition is an important aspect of theinvention SIIlCB IlZ permitsrapid and uniform wetting of the mass withthe solvent. With efiicient and properly sized commercial mixers, themixing time to attain said powdery condition usually falls in the rangeof about 5 to about 30 minutes.

Upon attaining said powdery condition, the solvent is introduced in anyconvenient manner so as to uniformly wet the powder. The amount ofsolvent which is used range of to 70 parts by weight per 100 parts .byweight of binder component. A more preferred range is about 14- to about45 parts by werght of solvent for each 100 parts by weight of bindercornponent. Mixing is continued during and after the addition of thesolvent to insure uniform distribution of tne solvent in the powderymass. Sufficient mixing is employed to obtain a uniform intermediatedispersion or blend. 7 Usually the time required to add the solvent andto obtain said uniform intermediate dispersion is only of the order of 1to 5 minutes. It is to be noted that the amount of solvent employed isnot suflicient to obtain a solution of the binder component. Saidsolvent is employed in an amount sufficient to only soften the bindercomponentand' upon mixing or milling of the softened bindercomponent theabove-mentioned uniform intermediate dispersion of the sol-idingredients in the rubbery polymer results. Sometimes, depending uponthe amount of solvent used, the powdery mass tends to agglomerateinto'individual balls or agglomerates which tendto increase in size uponcontinued mixing. However, said individual balls or agglomerates areuniform dispersions of the solid ingredients in the rubbery polymer andit is not necessary to continue mixing at this stage until all of theindividual agglomerated particles have been consolidated into one mass.

After said uniform intermediate dispersion is obtained, the remainder ofthe oxidizer component and/or other solid ingredientsare added withsufiicient mixing to obtain a uniform final dispersion of said solidingredients in the rubbery polymer. Since the invention finds itsgreatest application in the preparation of solid composite typepropellants having high oxidizer contents, the amount of oxidizer addedas the last increment is usually sufficient -to increase the totaloxidizer content of the propellant composition to a value within therange of about 90 to 96 weight percent of the total composition. Asindicated above, the oxidizer component can be divided into any suitablenumber of increments and added incrementally, or it can be added slowlyin a continuous manner. If desired the other solid dry ingredientsemployed in the propellant composition can be blended with the oxidizercomponent and the blend divided into increments or added slowly in acontinuous manner. Or, if desired, said other solid dry ingredients canbe incorporated or blended with the last increment of oxidizercomponent.

After all of the oxidizer component and said other dry ingredients havebeen incorporated into the rubbery polymer with the aid of the solventas described above, the solvent is then removed. Solvent removal can beeffected conveniently by continued mixing in the mixing equipment underreduced pressure, preferably at pressures below millimeters of mercurywhereby said solvent is distilled from the propellant mixture. Becauseof the relatively small amount of solvent present, essentially completeremoval of the solvent can be effected within an hour or two, even attemperatures as low as 20 to C. If desired, the mixture can be heated toincrease the rate of solvent removal. Quaternizing agents or othercuring agents can be added to the propellant mixture before or after theremoval of the solvent. If said quaternizing'agents are added prior toremoval of the solvent, the temperature to which the composition isheated in order to effect solvent removal should be sufiiciently low soas to avoid rapid curing of the rubbery polymer. Generally temperaturesup to about 60 C. can be employed without danger.

After the solvent has been removed the propellant composition can beformed into propellant grains by extrusion or by compression molding,using conventional techniques known to those skilled in the art.

Any organic liquid having a boiling point at atmospheric pressure belowabout C., and which is capable of swelling or dissolving the rubberypolymer of the binder component, can be used as the solvent in thepractice of the invention. Solvents having a boiling point as low as 20C. or lower can be used if means are provided to prevent escape ofsolvent vapors such as carrying out the solvent addition and mixingunder pressure. The preferred solvents have a boiling point of about 40to about 60 C. for convenience in handling. Suitable solvents for use inthe practice of the invention include the various hydrocarbon liquidssuch as hexane, heptane, octane, nonane, cyclohe-ptane, cyclohexane,benzene, toluene, xylene, methylcyclohexane, various naphthas,kerosenes, and the like which have been stripped of high boilingcomponents. Other suitable solvents include the chlorinated hydrocarbonssuch as carbon tetrachloride, 1,2-dichloroethylene, l, 2-dichloroethane,and the like.

The term rubbery polymer as used herein and in the claims, unlessotherwise specified, includes natural rubbar and all rubberypolymers ofolefins and diolefins which are prepared by either mass or emulsionpolymerization. Some examples of suitable rubbery polymers arepolybutadiene, polyisobutylene, polyisoprene, c0- polyrners ofisobutylene and isoprene, copolymers of conjugated dienes'withcomonorners such as styrene, and copolymers of conjugated dienes withpolymerizable heterocyclic nitrogen bases. Said copolymers of conjugateddienes with polymerizable heterocyclic bases comprise a preferred classof rubbery polymers for use in the binder component of the propellantsof the invention. A presently preferred rubbery polymer is a copolymerof 1,3- butadiene with Z-methyl-S-vinyl pyridine.

Said preferred class of rubbery polymers prepared by copolymerizing aconjugated diene with a heterocyclic nitrogen base, as well as the otherrubbery polymers, can

vary in consistency from very soft rubbers, i.e., materials which aresoft at room temperature but will show retraction when relaxed, to thosehaving a Mooney value (ML4 at 212 F.) up to 100. Therubbcry polymersmost frequently preferred in the practice of the invention have Mooneyvalues in the range between IOand 60. :They may be prepared by anypolymerization methods known to the art, e.g., mass or emulsionpolymerization. One convenient method for preparing said preferredcopolymers is by emulsion polymerization at temperatures in'the rangebetween 0 and F. Recipes such as the iron pyrophosphate-hydroperoxide,either sugar-free or containing sugar, 1116.5111fOXY1'3tC, and thepersulfate recipes are among those which are applicable. It .is'advantageous to polymerize to high conversion as the unreactedvinylpyridine monomer is difficult to remove by stripping.

The conjugated dienes employed are those containing from 4 to 10 carbonatoms per molecule and include 1,3-butadiene, isoprene,2-rnethyl-l,3-butadiene, and the like. Various alkoxy, such as methoxyand ethoxy and cyano derivatives of these conjugated dienes, are alsoapplicable. Thus, other dienes, such as phenylbutadiene,2,3-dimethyl-l,3-hexadiene, 2 methoxy-3-ethylbutadiene, 2ethoxy-3-ethyl-1,3-hexadiene, 2 cyano-1,3-butadiene, are alsoapplicable.

Instead of using a single conjugated diene, a mixture of conjugateddienes can be employed. Thus, a mixture of 1,3-butadiene and isoprenecan be employed as the conjugated diene portion of the monomer system.

The polymerizable .heterocyclic nitrogen bases which are applicable forthe production of the polymeric materials are those of the pyridine,quinoline, and isoquinoline series which are copolymerizable with aconjugated diene and contain one, and only one,

T substituent wherein R is either hydrogen or a methyl group. That is,the substituent is either a vinyl or an alpha-methylvinyl (isopropenyl)group. Of these, the compounds of the pyridine series are of thegreatest interest commercially at present. Various substitutedderivatives are also applicable but the total number of carbon atoms inthe groups attached to the canbon'atoms of the heterocyclic nucleusshould not be greater than because the polymerization rate decreasessomewhat with increasing size of the alkyl group. Compounds where thealkyl substituents are methyl ,and/ or ethyl are available commercially.

These heterocyolic nitrogen bases have the formula where -R is selectedfrom the group consisting of hydrogen, alkyl, vinyl, alpha-methylvinyl,alkoxy, halo, hydroxy, cyano, aryloxy, aryl, and combinations of thesegroups such as haloalkyl, alkylaryl, hydroxyaryl, and the like; one andonly one of said groups being selected from the group consisting ofvinyl and alpha-methylvinyl; and the total number of carbon atoms in thenuclear substituted groups being not greater than 15. Examples of suchcompounds are 2-v-inylpyridine; 2-vinyl-5-ethylpyridine;Z-methyl-S-vinylpyridine; 4-vinylpyridine;2,3,4-trimethyl-S-vinylpyridine; 3,4,5,6 tetramethyl-Z-vinylpyridine;3-ethyl-5-vinylpyridine; 2,6-diethyl-4-vinylpyridine;2-isopropyl-4-nonyl-5-vinylpyridine; 2-methyl-5-undecyl-3-vinylpyridine; 2,4-dimethyl-5,6-dipentyl-3-vinylpyridine; 2-decyl-5-(alpha-methylvinyl) pyridine; 2-vinyl-3-methyl- 5 -ethylpyn'd=ine;2-methoxy-4-chloro-6-vinylpyridine; 3- vinyl-S-ethoxypyridine;2-vinyl-4,S-dichloropyridine- 2 alpha-methylvinyl)-4-hydroxy-6-cyanopyridine; 2-vinyl- 4 phenoxy-S-methylpyridine; 2cyano-S-(alpha-methylvinyl) pyridine; 3-vinyl-5-phenylpyr-idine;2-(para-methylphenyl)-3-vinyl-4-methylpyridine; 3-vinyl 5(hydroxyphenyl)-pyn'dine; 2-vinylquinoline; 2-vinyl-4-ethylquinoline;3-vinyl-6,7-di-n-propylquinoline; 2-methyl-4-nonyl- 6-vinylpyridine; 4line; 3-vinylisoquinoline; 1,6-d-imethyl-3-vinylisoquinoline;2-vinyl-4-benzylquinoline; 3-vinyl-5-chloroethylquinoline-3-vinyl-5,6-dichloroisoquh1oline; 2 vinyl-6-ethoxy- 7-nrethylquinoline;3-vinyl-6-hydroxymethy1isoquinoline; and the like.

Another preferred rubbery polymer which can be employed in the binder ofthe solid propellant composition of this invention isa copolymer of1,3-butadiene with styrene. Such copolymers are commonly known in theart as GH-S rubbers. Said GR-S rubbers can be pre-- pared by any or thewell known methods employing well known recipes. Any of the well knownGR-S rubbers containing from 1 to 2 and up to about par-ts of styrene(alpha-methylvinyl) -8-dodecylquinocan be used in the practice of theinvention. The GR-S rubber designated as 1505 is one preferred copolymerfor use in the practice of the invention. 6R4 1505 can be prepared bycopolymerizing 1,3-butadiene with styrene at 41 using a sugar free, ironactivated, rosinacid emulsified system. A charge Weight ratio ofbutadiene to styrene is /10 and the polymerization is allowed to go toapproximately 52 percent completion. The copolymer is then salt acidcoagulated and usually has a mean raw Mooney value (ML-4) of about 40.Said copolymers usually have a bound styrene content of about 8 weightpercent. Further details regarding the preparation of GR-S rubbers canbe found in Industrial and Engineering Chemistry, 40, pages 769777(1948) and United States Patents 2,583,277; 2,595,892; 2,609,362;2,614,100; 2,647,109; and 2,665,269.

The binder contains rubbery polymers of the type hereinbefore describedand, in addition, there can be present one or more reinforcing agents,plasticizers, Wetting agents, and antioxidants. Other ingredients whichare employed for sulfur vulcanization include a vulcanizationaccelerator, a vulcanizing agent, such as sulfur, and an acceleratoractivator, such as zinc oxide. The finished binder usually containsvarious compounding ingredients. Thus, it will be understood that hereinand in the claims, unless otherwise specified, the term binder isemployed generically and includes various conventional compoundingingredients. The binder content of the propellant composition willusually range from 4 to 25 percent by weight.

The rubbery copolymer comprising a conjugated diene and a polymerizableheterocylic nitrogen base can also be cured by a quaternization reactionby incorporating therein a quaternizing agent and subjecting theresulting mixture to quaternizing conditions of temperature. Thus, thebinder component can also contain a quaternizing agent. Suitablequaternizing agents include, among others, the following: alkyl halidessuch as methyl iodide, and methyl bromide; alkylene halides such asmethylene iodide, and ethylene bromide; substituted alkanes such aschloroform, bromoform, and alkyl sulfates such as methyl sulfate; andvarious substituted aromatic compounds such as benzoyl chloride, methylbenzene sulfonate, benzo-trichloride, benzyl chloride, benzal chloride,paraxylenehexachloride, and the like. The quaternizing temperature isusually in the range from 0 to 250 F., although temperatur'es outsidethis range can be used.

A general formulation for the binder component of the propellantcomposition of the invention is as follows:

Parts by weight Rubbery polymer Reinforcing agent 0-50 Plasticizer 0100Wetting agent 0-10 Antioxidant 0-3 Vulcanization accelerator 0-5 Sulfur0-2 Quaternizing agent 025 Metal oxide 0-5 (saturated polymerized hydropreferred that the plasticizers be -.One presently preferred plasticizeris. a liquid polybutadiene prepared by mass polymerization in thepresence. of finely divided sodium as the catalyst according to themethod of. Crouch 2,631,175. Broadly, such plasticizers which can beusedin accordance with this invention comprise liquid polymers preparedfromconjugated diolefin hydrocarbons such as 1,3-butadiene and isoprene, theliquid polymers having a viscosity of 100 to 5000 Saybolt Furol Secondsat 100 F. Polymers having a viscosity from about 1000 to about 2500Saybolt Furol Seconds are presently preferred. These liquid polymers canbe prepared by emulsion polymerization using large amounts of modifiersin accordance with the teaching of Frolich et al. 2,500,983 although,they are preferably prepared by the method set forth in Crouch2,631,175. The latter method comprises mass polymerization in thepresence of finely divided alkali metal and/ or alkali metal hydride'such as sodium, potassium, lithium, sodium hydride, potassium hydrideand lithium hydride. Polymers thus prepared contain no modifiers orviscosity controlling agent and. they are also free of materials whichwould act as inhibitors such as antioxidants and shortstops. Finelydivided catalyst is used, preferably having a particle size below 200microns, and generally below 100 microns in the range of 40 to 80microns. The amount of catalyst employed usually does not exceed 2 partsby weight of the total monomer charged, preferably in the range of 0.5to 1.5 parts by weight per 100 parts monor'ner. A more completedescription of the process is set forth in the Crouch patent identifiedabove.

Another presently preferred plasticizer for use in the propellantcompositions of the invention is Philrich 5, a rubber extender andprocess oil available commercially from Phillips Petroleum Company. SaidPhilrich 5 is a highly aromatic heavy petroleum residual oil. Typicaltests on said Philrich 5 are:

Nitrogen bases 11.0 First acidafiins 19.0 Second acidafiins 61.0Paraifins 9.0

Wetting agents aid in deflocculating or dispersing the oxidizer. AerosolOT (dioctyl ester of sodium sulfosuccinic acid), lecithin, and Duomeen Cdiacetate (the diacetate of trimethylenediamine substituted by a coconutoil product) are among the materials which are applicable.

Antioxidants which can be employed include Flexamine (physical mixturecontaining 65' percent of a complex diarylamine-ketone reaction productand 35 percent of N,N-diphenyl-p-phenylenediamine), phenylbeta-naphthylamine, "2,2 methylene bis(4 methyl 6 tert-butylphenol), andthe like. Rubber antioxidants, in general, can be employed or if desiredcan be omitted.

' Examples of vulcanizationaccelerators are those of the carbamate type,such as N,N-dimethyl-S-tert-butylsulfenyl dithiocarbamate andButyl-Eighh' Butyl-Eight is a rubber accelerator of the dithiocarbamatetype supplied by the R. F. Vanderbilt Company and described in Handbookof Material Trade Names by Zimmerman and Lavine, 1953 edition as a brownliquid; specific gravity 1.01; partially soluble in water and gasoline;and soluble in acetone, alcohol, benzol, carbon disulfide andchloroform. t

- It is to be understood that each of the various types of compoundingingredients canbe used singly or mixtures of various ingredientsperforming a certain function can be employed. It is sometimespreferred, for example, toaluse mixtures of plasticizers rather than asingle mate- 1'1 Frequently in the preparation of the binder componentAPI 11.6

among others, finely divided boron, and finely divided 8 the rubberypolymer is masterbatched with the reinforcf ing filler, mixed with'theanti-oxidant, and dried. The resulting masterbatch of polymer, filler,and anti-oxidant is stored and subsequently blendedas needed withothetingredients to form the binder component.

Oxidizers which are applicable in the solid propellant compositions ofthis invention are those oxygen-containing solids which readily give upoxygen and include, for example, ammonium, alkali metal, and alkalineearth metal salts of nitric, perchloric, and chloric acids,and thereof,Ammonium nitrate and ammonium perchlorate are'the preferred oxidizersfor use in the solid propellants of this invention. Other specificoxidizers include nitrate, potassium perchlorate, lithium chlorate,calcium nitrate, barium perchlorate, and strontium chlorate. Mixtures ofoxidizers are also applicable. In the preparation of the solid rocketpropellant compositions, the oxidizers are ground to a particle size,preferably within the range between 20 and 200 microns average particlesize. The most preferred particle size is from 40-60 microns. The amountof solid oxidizer used is a major amount of the total composition and isin the range of to 96 percent by weight of the total propellantcomposition.

When ammonium nitrate is used as the oxidant component, a phasestabilized ammonium nitrate is frequently used. One methodof phasestabilizing ammonium nitrate is to admix about 10 parts of a potassiumsalt (usually potassium nitrate) with about parts of ammonium nitrate,along with some water, heating the mixtur to about 140 F., dry, and thengrind to the desired patricle size.

It is also within the scope of the invention to employ solid organicoxidizing compounds as a portion of the oxidizer component. Examples ofsaid organic oxidizing compounds include, among others, the following:cyclotrimethylene trinitramine, pentaerythritol tetranitrate,cyanoguanidine, nitroguanidin'efand guanidine nitrate. Said organicoxidizing compound can be used in an amount ranging from 0 to 10 solidinorganic oxidizing compound, or, stated another way from about 0 toabout 10 weight percent of the total oxidizer content. The organicoxidizing compound replaces a like amount of the inorganic oxidizingcompound. Thus, the total amount of solid oxidizing compound in thepropellant composition remains within the range of 75 to 96 weightpercent of the total propellant composition.

In some instances it is desirable to employ a burning rate catalyst inthe propellant compositions of the invention. Any suitable burning ratecatalyst can be used in the' propellant compositions of the invention.Burning rate catalysts applicable in the invention include ammoniumdichromate and metal ferrocyanides and ferricyanides. Hamburg, Chinese,Paris, and Milori blue, soluble ferric ferrocyanide, such as solubleBerlin or Prussian blue which contains potassium ferric ferrocyanide,and ferric ferrocyanide which has been treated with ammonia, are

among the materials which can beused. Ferrous ferri-- cyanide (Turnbullsblue) is also applicable. A particularly effective burning rate catalystis Milori blue which is pigment similar to Prussian blue buthaving aredtint.

and isprepared by the oxidation of a paste of potassium ferrocyanide andferrous sulfate. Other metal compounds such as nickel and copperferrocyanides can also be employed. The amount of burning rate catalystused in the propellant compositions of the invention can be withintherange of 0 to 5 weight percent of the total composi- 1.101 1.

It is also within the scope of the invention to include in thepropellant composition high energy fuels or pro pellant additives toincrease the specific impulse of'the propellant. Examples of said highenergy fuels include,

metals such as aluminum, magnesium, iron, and alloys of parts for each100 parts of Ferric ferrocyanides, such as Prussian, Berlin,-

9 said metals. Said high energy fuels or additives are usually used inamounts ranging from to weight percent of the total propellantcomposition.

The following examples will serve to further illustrate the invention.

EXAMPLE I A rubbery copolymer was prepared by emulsion polymerization of1,3-butadiene and 2-methyl-5-vinylpyridine at 41 F. The polymerizationrecipe was as follows:

Recipe Parts by weight 1,3-butadiene 90 2-methyl-5-vinylpyridine 10Water 200 Potassium soap 6 Potassium chloride 0.1

A total of 55 runs were made using the above recipe. The averageconversion for these runs was 85 percent in 17.0 hours. Thepolymerization was shortstopped with 0.15 parts by weight per 100 partsby weight of rubber of potassium dimethyl dithiocarbamate, and 1.75parts by weight per 100 parts by weight of rubber ofphenylbeta-naphthylamine was added as a stabilizer. The latex wasmasterbatched with 19.5 parts by weight of a low abrasion furnace carbonblack per 100 parts by Weight of rubber. The black masterbatch was thencoagulated with acid, the crumb was washed with water, and then dried.

The carbon black content of the above-described copolymer product wasincreased to 22 parts by weight per 100 parts by weight of rubber bymilling an additional 2.5 parts of said carbon black into saidcopolymer.

The thus prepared copolymer masterbatch wa placed in a Baker-Perkinsmixer and given a preliminary milling. Three parts of Flexamine per 100parts of copolym'er and 20 parts of Butarez 25 per 100 parts ofcopolymer were then milled into said copolymer masterbatch.

The thus prepared rubber masterbatch was used to prepare a propellanthaving the following composition:

1 Physical mixture containing 65 percent of a complex diarylamine- 153$;ereaction product and 35 percent of N,N-diphenyLp-pheirylene- 2 Liquidpolymer prepared by mass polymerization of 1,8-butadiene using finelydivided sodium as catalyst The viscosity at 100 F. is about 2500centipoises.

The oxidizer was a blend prepared by mixing 330 grams of ammoniumnitrate and 987 grams of ammonium perchlorate, each having a weightaverage particle size, as estimated from screen analysis, of about 40microns. The oxidizer was divided into six approximately equal portions.

Said rubber masterbatch was placed in a Baker-Perkins mill, and fiveportions of the oxidizer were added separately over a to minute period.Each portion was mixed to achieve uniform dispersion before addition ofthe next portion. During addition of the fifth portion the mixturebecame powdery. This powder mass represented a blend of 15 percent byweight of binder and percent by weight of oxidizer.

Before addition of the sixth and last increment of oxidizer ml. ofmethylcyclohexane was added to the powdery mass with mixing for a periodof 1 to 2 minutes whereupon the mixture was converted to a slightlytacky mass. The last increment of oxidizer was than added and mixed forabout 3 minutes so as to obtain a uniform blend. The p-xylenehexachloride was then uniformly incorporated into said blend. Mixing wasthen continued for about 10 minutes while maintaining the pressure belowabout one millimeter of mercury pressure within the mixer. Themethylcyclohexane was thus removed by distillation. The resultingproduct had no odor and could be crumbled by pressing between thefingers. When rubbed between the fingers the product felt slightlytacky. The product was moldable. Tubular grains having an CD. of 3inches and an ID. of 1.5 inches and a length of 4 inches were formed ina press. Pressure on the order of 10,000 p.s.i.g. was applied to thepropellant composition by means of a piston while forming the propellantgrain. The grain was readily removed from the mold, had smooth surfacesand was a uniform blend.

EXAMPLE 11 Another test was made as described above except that.

The above examples illustrate the preparation of com-- pression moldedpropellant grains from propellant mixes prepared in accordance with theinvention. Other tests have shown that high oxidizer content propellantmixes prepared according to the invention can be extruded without thenecessity of incorporating extrusion aids.

As will be evident to those skilled in the art, various modifications ofthe invention can be made or followed in the light of the abovedisclosure without departing from the spirit or scope of the invention.

I claim:

1. A method for preparing a solid composite type propellant whereinfinely divided solid ingredients comprising an oxidizer componentselected from the group consisting of solid inorganic oxidizing salts,mixtures of said inorganic salts, and mixtures of a solid inorganicoxidizing salt with a solid organic oxidizing compound selected from thegroup consisting of cyclotrimethylene trinitramine, pentaerythritoltetranitrate, cyanoguanidine, nitroguanidine, and guanidine nitratewherein the mixture contains up to 10 parts by weight of said organiccompound per 100 parts by weight of said inorganic salt, are

uniformly dispersed in a binder component comprising a rubbery polymerselected from the group consisting of natural rubber, synthetic rubberpolymers, and mixtures thereof, which method comprises, in combination,the

steps of: mechanically mixing said solid ingredients into a said bindercomponent until a powdery mass is obtained;

then incorporating a low boiling organic solvent selected from the groupconsisting of hexane, heptane, octane, nonane, cycloheptane,cyclohexane, benzene, toluene, xylene, methylcyclohexane, naphthafractions, kerosene fractions, carbon tetrachloride1,2dichloroethyl-ene, and 1,2-dichloroethane, in an amount suflicient tosoften said binder component, into said powdery mass with sufiicientmechanical mixing to form a uniform intermediate dispersion of saidsolid ingredients in said binder composolid inorganic oxidizing salts,mixtures of said inorganic salts, and mixtures of a solid inorganicoxidizing salt with, a solid organic oxidizing compound selected fromthe group consisting ofcyclotrimethylene trinitramine, pent-aerythritoltetranitrate, cyanoguanidine, nitroguanidine, and guanidine nitratewherein the mixture contains up to parts by weight of said organiccompound per 100 parts by weight of said inorganic salt, areuniformlydispersed in a binder component comprising a rubbery polymer selectedfrom the group consisting of natural rubber, synthetic rubber polymers,and mixtures thereof, the improvement which comprises, in combination,the steps of: mechanically mixing a sufiicient quantity of said solidingredients into said binder component to obtain a powdery mass; thenincorporating a low boiling organic solvent selected from the groupconsisting of hexane, heptane, octane, nonane, cycloheptane,cyclohexane, benzene, toluene, xylene, methylcyclohexane, naphthafractions, kerosene fractions, carbon tetrachloride,1,2-dichloroethylene, and 1,2-dichloroethane, in an amount sufficient tosoften said binder component, into said powdery mass with .sufiicieritmechanical mixing to form an intermediate uniform dispersion of saidsolid ingredients in said binder component; then uniformly dispersingwith mechanical mixing an additional increment of said solid ingredientsinto said intermediate dispersion to form a final uniform dispersion ofsaid solid ingredients in said binder component; and then evaporatingsaid solvent from said final dispersion.

3. A method for preparing a solid composite type propellant comprisingfrom 75 to 96 weight percent of an oxidizer component selected from thegroup consisting of solid inorganic oxidizing salts, mixtures of saidinorganic salts, and mixtures of a solid inorganic oxidizing salt with asolid organic oxidizing compound selected from the group consisting ofcyclotrimethylene trinitramine, pentaerythritol tetranitrate,cyanoguanidine, nitroguanidine, and guanidine nitrate wherein themixture contains up to 10 parts by Weight of said organic compound per100 parts by weight of said inorganic salt, and from to 4 weight percentof a binder component comprising a rubbery polymer having a Mooney value(ML-4 at 212 F.) in the range of 10 to 100 and being selected from thegroup consisting of natural rubber, synthetic rubber polymers, andmixtures thereof, which method comprises,

in combination, the steps of: mechanically mixing successive incrementsof said oxidizer component into said binde'r'com'ponent until a powderymass is obtained; then incorporating from 10 to 70 parts by weightper100 parts by weight of said binder component of an organic solventhaving a boiling point below about 120 C. and selected'from the groupconsisting of hexane, heptane, octane, nonane, cycloheptane,cyclohexane, benzene, toluene, xylene, methylcyclohexane, naphthafractions, kerosene fractions, carbon tetrachloride,1,2-dichloroethylene, and 1,2-dichloroethane, into said powdery masswith suificient mechanical mixing to form a uniform inter- I mediatedispersion of said oxidizer component insaid binder component; thenmechanically mixing at least. one additional increment of said oxidizercomponent into said intermediate dispersion withsuflicient mixing to ob-I tain a final uniform dispersion of said oxidizer component in saidbindercomponent; and then evaporating said solvent from said finaldispersion.

4. A method for mixing a composite type propellant, which method,comprises, in combination, the steps of:

mechanically mixing a portion of the oxidizer component 7 1;? with thebinder component to obtain a powdery mass said oxidizer component beingselected from the group consisting of solidinorganic oxidizing salts,mixtures of said inorganic salts, and mixtures of a solid inorganicoxidizing salt with a solid organic oxidizing compound sea, lected fromthe group consisting of cyclotrimethylene trinitramine, pentaerythritoltetranitrate, cyanoguanidine, nitroguanidine, and guanidine nitratewherein the mixture contains up to 10 parts by weight of said organiccompound per parts by weight of said inorganic salt, and said bindercomponent being selected from the group consisting of natural rubber,synthetic rubber polymers, and mixturesthereof; then a low boilingorganic solvent se-' lected from the group consisting of hexane,heptane, octane, nonane, cycloheptane, cyclohexane, benzene, toluene,xylene, methylcyclohexane, naphtha fractions, kerosene fractions, carbontetrachloride, 1,2-dichloroethylene, and 1,2-dichloroethane, into saidpowdery mass with mechanical mixing in an amount sufficient to onlypartially dissolve said binder component; then mechanically mixing anadditional increment of said oxidizer component into said solventtreated powdery mass; and then evaporating said solventfrom the finalmixture.

.5. A method according to claim 1 wherein said oxidizer component is amixture of at least one solid inorganic oxidizing salt with at least onesolid organic oxidizing compound selected from the group consisting is acopolymer of (a) a conjugated diene containing from 4 to 10 carbon atomsper molecule and (b) a substituted heterocyclic nitrogen base selectedfrom the group consisting of pyridine, quinoline, alikyl substitutedpyridine, and alkyl substituted quinoline wherein the total number ofcarbon atoms in the nuclear alkyl substituents is not more than 15, andwherein R is selected from the group consisting of hydrogen and a methylradical.

7. A method according to claim 6 wherein said copolymer is a copolymcrof 1,3-butadiene with Lmethyl-S- vinylpyridine.

8. A method according to claim 1 wherein said rubbery polymer is acopolymer prepared butadiene with styrene. a 7

' 1 References Cited the file of this patent i V 'j UNITED STATESPATENTS OTHER REFERENCES Chem; and Eng. News, Oct. 7, 1957, pp. 62, 63..

Baker: Missiles and Rockets, vol. 4, No. 6, Aug. 11, 1958-, pp. 45-47.

Kit et al.: Rocket Propellant Handbook, The M Millan 00., New York(1960), p. 201. V

by copolymerizing 1,3-

1. A METHOD FOR PREPARING A SOLID COMPOSITE TYPE PROPELLANT WHEREINFINELY DIVIDED SOLID INGREDIENTS COMPRISING AN OXIDIZER COMPONENTSELECTED FROM THE GROUP CONSISTING OF SOLID INORGANIC OXIDIZING SALTS,MIXTURES OF SAID INORGANIC SALTS, AND MIXTURES OF A SOLID INORGANICOXIDIZING SALT WITH A SOLID ORGANIC OXIDIZING COMPOUND SELECTED FROM THEGROUP CONSISTING OF CYCLOTRIMETHYLENE TRINITRAMINE, PENTAERYTHRITOLTETRANITRATE, CYANOGRANIDINE. NITROGUANIDINE, AND GUANIDINE NITRATEWHEREIN THE MIXTURE CONTAINS UP TO 10 PARTS BY WEIGHT OF SAID ORGANICCOMPOUND PER 100 PARTS BY WEIGHT OF SAID ORGANIC SALT, ARE UNIFORMLYDISPERSED IN A BINDER COMPONENT COMPRISING A RUBBERY POLYMER SELECTEDFROM THE GROUP CONSISTING OF NATURAL RUBBER, SYNTHETIC RUBBER POLYMERS,AND MIXTURES THEREOF, WHICH METHOD COMPRISES, IN COMBINATION, THE STEPSOF; MECHANICALLY MIXING SAID SOLID INGREDIENTS INTO SAID BINDERCOMPONENT UNTIL A POWDERY MASS IS OBTAINED THEN INCORPORATING A LOWBOILING ORGANIC SOLVENT SELECTED FROM THE GROUP CONSISTING OF HEXANE,HEPTANE, OCTANE, NONANE, CYCLOHEPTANE, CYCLOHEXANE, BENZENE, TOLUENC,XYLENE, METHYLCYCLOHEXANE, NAPHTHAL FRACTIONS, KEROSENE FRACTIONS,CARBON TETRACHLORIDE 1,2-DICHLOROETHYLENE, AND 1,2-DICHLOROETHANE, IN ANAMOUNT SUFFICIENT TO SOFTEN SAID BINDER COMPONENT, INTO SAID POWDERYMASS WITH SUFFICIENT MECHANICAL MIXING TO FORM A UNIFORM INTERMEDIATEDISPERSION OF SAID SOLID INGREDIENTS IN SAID BINDER COMPONENT; THENMECHANICALLY MIXING AT LEAST ONE ADDITIONAL INCREMENT OF SAID SOLIDINGREDIENTS INTO SAID INTERMEDIATE DISPERSION WITH SUFFICIENT MIXING TOATTAIN A FINAL UNIFORM DISPERSION OF SAID SOLID INGREDIENTS IN SAIDBINDER COMPONENT; AND THEN EVAPORATING SAID SOLVENT FROM SAID FINALDISPERSION.